A significant number of people with chronic conditions had difficulty getting affordable insurance before Obamacare. The law dealt with the problem by prohibiting insurers from discriminating on the basis of health status. If you have a chronic condition, they have to sell you the same policy at the same rate they would offer someone in perfect health. That regulation raises the cost of health insurance for healthy people and thus discourages them from buying it. (It also creates an incentive for insurers to design policies that are more attractive to healthy than to sick people.)
When they tried to legislate a replacement to Obamacare in 2017, Republicans sought to let states relax that regulation. Under their proposal, states could have required insurers to offer the same policies at the same rates to all customers, regardless of health status, so long as they had previously maintained coverage. That way, people would have had an incentive to purchase insurance while healthy, bringing premiums down. States would have been allowed to make this change only if they had shown that they had credible plans to take care of those who fell through the cracks.